Why cant I assign Bitmap to Image.Source?

Question

void VideoCaptureDevice_NewFrame(object sender, NewFrameEventArgs eventArgs)
        {
            pictureBox1.Source = (Bitmap)eventArgs.Frame.Clone();
        }

on Windows Form this works pictureBox1.Image= (Bitmap)eventArgs.Frame.Clone(); //But on Windows WPF-App not..

i found a Classs called IMAGE in System.Windows.Forms

pictureBox1.Image= (Bitmap)eventArgs.Frame.Clone();

and this Code line is full functional in Windows Forms

But in Windows WPF-APP it wont, first I tryed to change the .Image to .Source

But now it says "implizit Bitmap into pictureBox.Source cant be converted"